already complete in plants and animals comparatively
low in the scale, it at first makes little difference in the
development of the other parts of the individual. Among many lower
animals, and most plants, each individual develops within itself both
kinds of cells--that is, female and male. This union of the two sex
functions in one organism is known as hermaphroditism. There is little
doubt that it was once common to all organisms, an intermediate stage
in the sex-progress, after the differentiation of the sexes had been
accomplished.

Hermaphroditism must be regarded as a temporary or transitional
form.[40] It is found persisting in various degrees in many
species--snails, earth-worms, and leeches, for example, can act
alternately as what we call male and female. Other animals are
hermaphrodite in their young stages, though the sexes are separate in
adult life, as, for example, tadpoles, where the bisexuality of youth
sometimes linger into adult life. Cases of partial hermaphroditism are
very common, while in many species which are normally unisexual, a
casual or abnormal hermaphroditism occurs--this may be seen in the
common frog, and is frequent among certain fishes, when sometimes the
fish is male on one side and female on the other, or male anteriorly
and female posteriorly.[41]

There would seem to be a constant tendency to escape from these early
and experimental methods of reproduction, and to secure true sexual
union, with complete separation of the sexes and differences in the
parents. We have noticed the many instances of tiny complemental
males, in connection with hermaphrodite forms, which, as Darwin
states, must have arisen from the advantage ensuring cross-fertilisation
in the females who harbour them. Even among hermaphrodite slugs we
find very definite evidence of the advance of love; and in certain
species an elaborate process of courtship, taking the form of slow and
beautiful movements, precedes the act of reproduction.[42] Some
snails, again, are provided with a special organ, a slightly twisted
limy dart, which is used to stimulate sexual excitement.[43] What do
such marvellous manifestations, low down in the ladder of life, go to
prove, if not that there must be the closest identity between the
development of life and the evolution of love?

These examples of hermaphrodite love lead us forward to a further
step, where no reproduction takes place without the special activity
and conjugation o